The giant guide warned them to look out for the loose bowlders, saying that some of them could be sent crashing down the mountain almost by the pressure of a hand.
The dangers from these huge rocks were made apparent before they had passed beyond that region.
Frank's horse proved far more skillful in climbing, keeping close to Big Gabe's heels, and the others were left at a considerable distance, so it became necessary to pause once or twice for them to come up.
A nearly level bit of the mountain had been reached, and they were pausing before the next climb, when a rumbling jar was heard, and a cry of warning broke from the guide.
"Loose bowlder! Look out fer it, boy!"
The others were yet some distance away, so that Frank and Gabe were together, the boy being astride his heavily breathing horse.
With each moment the roaring grew louder, till it swelled to jarring thunder, and then past them shot a huge black mass, enveloped in a cloud of dust. This mass leaped down into the black depths of a great chasm that yawned close at hand.
Frank's horse was frightened and began to plunge. The boy tried to quiet the animal, which was no easy task. In its mad plunging the creature reached the edge of the chasm. Big Gabe leaped forward with a second shout of warning, but it came too late.
Horse and rider went over the brink!